I was bored so I tried making my own universe on algodoo with the easy setting ability of Attraction. So on this scene includes these profiled matters:
Darkish-brown small circles: Possibly hard metals, cooled down alloys of that type
Brownish average sized circles: Some kind of organic matter possibly, forms the earths crust
Greyish-brownish medium circles: Cooled rock, stone matter, cooled minerals
Yellow, red and orange circles: Possibly molten materials like that in the earths mantle and molten minerals
Dark red circles: Core* most thing should form around these.
Enjoy, possibly may not work well though... 
 
Comment of performence: After I tested it, it seems the 'core' matter allows certain massed to be their 'own' mass and stay put with themselves rather then being affected by other masses, larger or smaller.
Also, the lose matter could represent a badly scaled form of asteroid matter or other loose type.
It also provides somewhat realistic collisions when certain masses collide. While making this, I made a highly dense form which resulted in explosive porportions. When you collide a small object at high speeds with a large mass, it could be quite devastating. I hope you enjoy it. 
